Simplify the following expression: $k = \dfrac{30cb - 10b^2}{10cb} - \dfrac{25ab - 10cb}{10cb}$ You can assume $a,b,c \neq 0$.
Solution: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{30cb - 10b^2 - (25ab - 10cb)}{10cb}$ $k = \dfrac{40cb - 10b^2 - 25ab}{10cb}$ The numerator and denominator have a common factor of $5b$, so we can simplify $k = \dfrac{8c - 2b - 5a}{2c}$